DESCRIPTION (adapted from the application) The goal of this proposal is to develop the gene therapy technology to replace the genetic defect in Crigler-Najjar Syndrome type I and improve the efficacy of adenoviral liver directed gene therapy in the Gunn rat animal model of congenital non-hemolytic unconjugated hyperbilirubinemia, this proposal is linked to K08 DK02438. Crigler-Najjar syndrome type 1, familial non-hemolytic jaundice and kernicterus, is a fatal disease, which can potentially be cured by genetic complementation. The disease results from a genetic defect in the enzyme responsible for glucuronidation of bilirubin. In its severest form, bilirubin accumulates in the serum leading to kernicterus and death. Features of this disease which make it an ideal candidate for liver directed gene therapy include: a) adenovirus mediated gene transfer of HUG Br 1 results in in vivo complementation of the disease, b) the biochemical, genetic, pathophysiological and clinical aspects of Crigler-Najjar syndrome type I have been extensively studied and are well described, c) phenotypic correction may be achieved with correction of substantially less than 100% of normal gene activity, d) an authentic animal model of human disease with an analogous hepatic metabolic deficiency, the Gunn rat, is readily available, e) no effective conventional therapy exists for Crigler-Najjar syndrome type I short of liver transplantation, and f) even partial, year-long correction may have clinical benefit. Adenovirus vector mediated gene transfer of a human bilirubin glucuronosyltransferase cDNA (HUG Br 1) is able to reverse the hyperbilirubinemia in Gunn rats for at least one year. The hypothesis to be tested is whether specific changes in the adenovirus vector sequence designed either to decrease expression of adenoviral proteins and vector immunogenicity and/or overexpression of a "MHC decoy" protein can augment HUG Br 1 gene can diminish immune responses in the Gunn rat. The mechanism of transgene persistence with the endogenous ribosomal promoter as opposed to the virus derived CMV promoter will be studied. The experimental design employs multiple modalities to detect gene transfer so that a drop in serum bilirubin may be correlated with other, more specific measures of gene transfer. This proposal includes several novel interventions designed to augment expression of the transgene leading to increased efficacy of in vivo adenovirus gene therapy. The results obtained in this model should prove valuable to the development of liver directed gene therapy for other genetic and acquired diseases.